Abstract 18806: Cofilin Is A Negative Regulator Of G-protein Independent β-arrestin Signaling
Cofilin is a known regulator of actin remodeling. Accumulating evidence indicate that Cofilin may be an active participant in regulating signal transduction independent of actin remodeling. Since it is known that Cofilin interacts with β-arrestin, we hypothesized that Cofilin regulates β-arrestin mediated G-protein independent β-Adrenergic receptor (βAR) signaling. To test whether cofilin regulates βAR signaling, we generated cofilin mutants that mimic constitutively active (S3A) and inactive (S3D) proteins. Isoproterenol (ISO) stimulation of β2AR stable HEK 293 cells co-expressing wild type (Wt), S3A and S3D cofilin mutants showed differential ERK activation. Significant ERK activation was observed with S3D mutant that was markedly reduced in cells expressing S3A cofilin. Expression of Wt resulted in reduced ERK activation consistent with our observation that Wt cofilin undergoes dephosphorylation following ISO stimulation. However, EGF mediated ERK signaling was found to be unaffected by status of Cofilin phosphorylation. Agonist mediated β-arrestin-GFP translocation to the plasma membrane was markedly reduced in presence of Wt or S3A mutant that was completely rescued in the presence of S3D Cofilin potentially accounting for the differential ERK activation. Co-immunoprecipitation studies showed enhanced binding of β-arrestin with Wt or S3A mutants compared to S3D Cofilin. In contrast, S3D bound minimally to arrestin indicating that higher binding by S3A (active Cofilin) inhibits β-arrestin mediated ERK activation. Depletion of β-arrestin1/2 by siRNAs in cells stably expressing S3D Cofilin significantly abrogated constitutive as well as agonist stimulated β-arrestin mediated ERK activation. End-stage human heart failure samples showed significant ERK activation (pERK) associated with higher levels of phospho-cofilin (inactive cofilin) compared to non-failing controls consistent with our observations in cellular studies. In conclusion, activation status of Cofilin is decisive in determining β-arrestin mediated βAR signaling with potential implications in cardio-vascular physiology as it has been recently shown that β-arrestin dependent transactivation is beneficial in conditions of deleterious cardiac stress.
- © 2010 by American Heart Association, Inc.